Metrology measurements are used in many environments for controlling system processes. For example, in semiconductor manufacturing environments, metrology measurements are frequently used to confirm that products are defect free and that the process is operating within the specified parameters. Sometimes such measurements are also used as an output feedback signal for model-predictive control algorithms that regulate the process.
In a typical semiconductor manufacturing environment, metrology measurements are made across the wafer randomly. The randomly selected measurement points are usually somewhat correlated, therefore they provide redundant information. Stated another way, it is possible to obtain the same amount of information without requiring as many measurements. Since metrology measurements are often expensive to make, it would be useful to have a way of obtaining metrology measurements that contains (or, as used throughout this specification, observes) more information with a smaller number of measurements.